In order to increase the effectiveness of modern artillery vehicles and reduce collateral damage, guidance systems are employed to navigate artillery vehicles during travel. After launch of an artillery vehicle, the artillery vehicle may rotate on an axis parallel to the path of travel. Since a spin rate of an artillery vehicle affects the travel of an artillery vehicle, guidance systems utilize spin rate data to guide the vehicle to a desired endpoint.
Conventional guidance systems for artillery vehicles use precalculated aiding data or onboard inertial sensors to determine the vehicle spin rate. Precalculated aiding data utilizes models of flight dynamics to determine the spin rate of a vehicle. A problem associated with precalculated aiding data is potential for large errors associated with the spin rate calculation in off-nominal conditions. Additionally, precalculated aiding data must be customized for each launch configuration.
Inertial sensors utilize systems within a vehicle to determine a spin rate. For instance, inertial sensors may include components within a vehicle housing, such as gyroscopes and accelerometers of the varieties known in the art for determining a vehicle spin rate. However, inertial sensors for determining the spin rate of a vehicle have inherent disadvantages when used in applications such as artillery vehicles. Inertial sensors add weight and volume to the already constrained space of an artillery vehicle. Inertial sensors also suffer from sensitivity to the high g-force and vibration environment found in artillery applications limiting accuracy performance and reliability while complicating system implementation. Further, current methods for obtaining spin rate in artillery vehicles increase the complexity of the vehicle by increasing the number of systems required to determine the spin rate, either internally (e.g., within the vehicle housing) or external to the vehicle.
Doty et al. in U.S. Pat. No. 6,520,488 describes a system to track the rotation angle of a spinning vehicle utilizing GPS. However, this system must be initialized with an estimate of rotation rate to allow a servo to track the roll angle. If the approximate spin rate is not known, the system requires additional time to search for the spin rate or to measure the modulation frequency of the GPS correlator outputs. This requires additional time. In applications with short flight times, such as artillery shell guidance, short acquisition times are critical to performance. A technique to rapidly determine an accurate estimate of rotation rate is needed in these applications.
Consequently, a system, method, and apparatus for accurately measuring the spin rate of a vehicle, while imparting minimal weight and volume restrictions to the vehicle, and reducing the systemic complexity of the vehicle is necessary.